President's Address. 
51 
not, to fling aside results so laboriously and painfully obtained, and 
with a saddened heart to commence their work again. But I shall 
have occasion to allude to this topic further on, and I touch upon it 
now only for the purpose of showing that in a society like ours, where 
the number of J.abourers in each department is not very great, the 
records of a single year are a wholly unreliable test of the intellectual 
activity of our members. Tliis unavoidable defect may be supplied 
by the address of the President. The review of the progress of the 
Academy which he brings before you should be founded on an induc- 
tion sufficiently large to eliminate accidental disturbances, thus 
enabl'ng you to judge, with at least a high degree of probability, 
whether the institution be really advancing or retrograding. 
I would observe here,, also, that in order to estimate rightly the 
condition of an institution like this, we must look beyond the institu- 
tion itself. Without such an examination we may commit the serious 
mistake of attributing to our o wn merit or default that which is really 
due to the general condition of some one branch of science. Eor progress 
in each department is not, any more than success in individual labours, 
uniform or even constant. In every such department there are periods 
of rapid advance and periods almost of stagnation — times when 
discoveries crowd upon us with a rapidity which is absolutely dazzling, 
and times when it might seem that the mine had been worked out. 
And therefore if we do not look beyond ourselves and our own labours, 
we may attribute that to our own culpable inactivity, which is really 
due to a general stagnation in some department of science. Or, on the 
other hand, we may take credit to ourselves for successful labour, 
when we are but sharing, and that imperfectly, in the general ad- 
vance — swept onward by a stream which is really passing us by. 
I take an example from our own history. We all know — many of 
us remember — how our meetings and our published records were 
adorned by the magnificent speculations of Professor M'CuUagh upon 
Physical Optics. Subsequent research has indeed shown that neither 
these nor any similar speculations faithfully represent J^ature; but 
no subsequent research can displace them from the position which 
they hold, as a combination, rarely surpassed, of mathematical and 
physical genius. Eut would it be reasonable that we should feel 
disappointment because we have nothing like them now ? I think not. 
For those were the days of Cauchy, and jS'eumann, and Green, and 
others, all intent upon the same problem — days, when the attention 
of the scientific world was largely given to the attempt to construct 
mechanical theories which might explain (in the popular sense of 
the word) the phenomena of light. But it is not so now. The study 
of Physical Optics has not ceased. On the contrary, I have but to 
pronounce the word ''spectroscope" to show that this study has 
become more active than ever. But it has taken a different direction ; 
more experimental, less theoretical. Mechanical theories of light 
have, if I may so express myself, gone out of fashion, and it would Le 
unreasonable to expect here an activity which, in this direction, has 
everywhere slackened. 
